Figure 1

(a) Fluorescent micrograph of reporter filaments in an actin network in the presence of rigor-HMM ($r_{\mathrm{ac}}=5$, $c_a=23.8\mu \mathrm{M}$, scale bar $10\mu \mathrm{m}$). (b) Electron micrograph of composite rigor-HMM/actin network ($r_{\mathrm{ac}}=5$, $c_a=9.5\mu \mathrm{M}$, scale bar $0.5\mu \mathrm{m}$). The addition of rigor-HMM does not result in the formation of actin bundles.Reuse & Permissions

Figure 2

(a) The frequency dependence of the moduli $G^{\prime }$ (full symbols) and $G^{\prime \prime }$ (open symbols) for a rigor-HMM/actin network at $c_a=19\mu \mathrm{M}$ and ■: $r_{ac}=660$, ●: $r_{\mathrm{ac}}=132$, ▴: $r_{\mathrm{ac}}=66$, ▾: $r_{\mathrm{ac}}=26$, ◂: $r_{\mathrm{ac}}=14$, ▸: $r_{\mathrm{ac}}=7$. With increasing HMM concentration the shape of $G^{\prime }(f)$ and $G^{\prime \prime }(f)$ remains unchanged; a distinct minimum in $G^{\prime \prime }(f)$ is observed for $r_{\mathrm{ac}}<200$. Inset: the frequency dependence of $\tan (\delta )=G^{\prime \prime }/G^{\prime }$ for the same rigor-HMM/actin networks. At low frequencies an increasing creep independent of $c_{\mathrm{HMM}}$ is observed. (b) The plateau modulus $G_0$ as a function of the cross-linker density. For all actin concentrations $G_0\sim r_{\mathrm{ac}}^{-1.2}$ (▸: $c_a=23.8\mu \mathrm{M}$, ◂: $c_a=19\mu \mathrm{M}$, ▾: $c_a=14.3\mu \mathrm{M}$, ▴: $c_a=9.5\mu \mathrm{M}$). At $r_{\mathrm{ac}}<3.3$ the filaments become saturated with HMM and as a result $G_0$ decreases slightly. Inset (symbols correspondingly): when $G_0(c_{\mathrm{HMM}})$ is normalized by $c_a^{11/5}$ all data points collapse onto one curve indicating that the network response is dominated by $L_c$.Reuse & Permissions

Figure 3

(a) The differential elastic modulus $K^{\prime }$ as a function of the deformation. With increasing rigor-HMM concentrations the slope in the nonlinear response regime clearly decreases ($c_a=19\mu \mathrm{M}$ and ●: $r_{\mathrm{ac}}=660$, ▾: $r_{\mathrm{ac}}=132$, ■: $r_{\mathrm{ac}}=26$, ◂: $r_{\mathrm{ac}}=14$, ▸: $r_{\mathrm{ac}}=7$). (b) When ${\gamma }_{\mathrm{crit}}$ is plotted against $c_{\mathrm{HMM}}$ a scaling of ${\gamma }_{\mathrm{crit}}\sim c_{\mathrm{HMM}}^{-0.4}$ is observed for all actin concentrations (▸: $c_a=23.8\mu \mathrm{M}$; ◂: $c_a=19\mu \mathrm{M}$; ▾: $c_a=14.3\mu \mathrm{M}$; ▴: $c_a=9.5\mu \mathrm{M}$). Inset (symbols correspondingly): the distance between cross-links $L_c$ as a function of $c_{\mathrm{HMM}}$ obtained from ${\gamma }_{\mathrm{crit}}$ assuming that $L_c=L_e$ at $r_{\mathrm{ac}}=3.3$.Reuse & Permissions